configure.ac: Remove obsolete macros

The newer macros that replace the obsolete ones are already present in configure.ac.

  * AC_PROG_LIBTOOL -> LT_INIT
  * AC_LANG_CPLUSPLUS -> AC_LANG([C++])

configure.ac

@@ -313,39 +313,25 @@ if test -d $curwd/gnu/lib ; then
    LDFLAGS="$LDFLAGS -L$curwd/gnu/lib"
 fi
 
-# ----------------------------------------
-# Check Compiler Characteristics and
-# configure automake. The two appear to
-# be intimately linked...
-# ----------------------------------------
-
-AC_PROG_LIBTOOL
-
 # ----------------------------------------
 # Additional checking of compiler characteristics
 # ----------------------------------------
 
 # Check Endianness. If Big Endian, this will define WORDS_BIGENDIAN
-# See also at end of this file, where we define INTEL_BYTE_ORDER
-# or MOTOROLA_BYTE_ORDER.
 AC_C_BIGENDIAN
 
 
 # ----------------------------------------
-# Check for programs we need
+# Init libtool
 # ----------------------------------------
 
-# Check where all the following programs are and set
-# variables accordingly:
 LT_INIT
 
 
 # ----------------------------------------
 # C++ related options
 # ----------------------------------------
 
-AC_LANG_CPLUSPLUS
-
 AC_MSG_CHECKING([if compiling with clang])
 AC_COMPILE_IFELSE(
 [AC_LANG_PROGRAM([], [[